Its presence and operations in the country flagrantly violate international law.

Assad calls US forces invaders, the same true of Turkey's military operating illegally cross-border, on the phony pretext of combatting terrorist groups Ankara supports, much like Washington uses them as imperial foot soldiers.

On Thursday, Syrian Assistant Foreign Minister Ayman Sousan denounced the presence of US forces in the country, calling it "utter aggression and a blatant violation of the international law."

He stressed his government will do all it can to free its territory from US occupation.

Syrian Foreign Minister Faisal Meqdad warned Turkey against "initiat(ing) combat operations in the Afrin area, that will be considered an act of aggression by the Turkish army," adding:

"The Syrian air defenses have restored their full force and they are ready to destroy Turkish aviation targets in Syrian Arab Republic skies."

Turkish forces have been operating illegally in Syria since August 2016, code-named Operation Euphrates Shield - launched on the phony pretext of combating ISIS, instead targeting Kurdish fighters, along with opposing Syrian sovereignty.

Despite calling its mission "successfully completed," Turkish forces operate cross-border at its discretion - in Iraq the same way, seeking control of their valued oil fields, a prize Erdogan long coveted.

He supports Washington's aim to topple Assad. Like Trump and his predecessors, he pretends naked aggression is combating terrorism - claiming ISIS and other terrorist groups he supports threaten Turkey.

Earlier he provided them safe haven cross-border and back to combat Syrian forces, perhaps still doing it covertly.

Ahead of Turkey's plan to prevent formation of Washington's border security force in northern Syria, residents in likely targeted Afrin, Manbij and other areas turned out in force, thousands protesting against Ankara's intention.

These areas are controlled by US-supported YPG fighters. Residents fear their communities will be transformed into battlegrounds, raped and destroyed like Raqqa.

Russia expressed concerns about US and Turkish intentions. Turkey's military chief met with his Russian counterpart in Moscow on Thursday - seeking support for his military's operations in Afrin and surrounding areas he's not likely to get.

Russia wants conflict winded down and resolved, not escalated. Russian lower house State Duma Defense Committee chairman Vladimir Shamanov said measures will be undertaken in response to Washington's plan to create a 30,000-strong border security force - "stand(ing) in direct confrontation" with Russia's interests.